Android：带有滑动的图库会跳过图像并且加载缓慢

Question

大家好，我是 Android 新手，所以请对我温柔一些:)，
我有一个画廊，我需要加载图像，我有很多图像，我已经通过使用 AsyncTask 解决了图像加载的性能。

现在我遇到了滚动画廊问题，它会跳过图像，而且看起来不太好。

现在我尝试实现我的自定义图库但没有成功，它只是行不通
现在我突然又有一个问题

final ScrollableGallery galleryView = (ScrollableGallery)findViewById(R.id.gallery); //always returns null

，你能解释一下为什么吗？

这是代码：

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.Gallery;

public class ScrollableGallery extends Gallery {

    public ScrollableGallery(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public ScrollableGallery(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public ScrollableGallery(Context context) {
        super(context);
    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {

        // limit the max speed in either direction
        if (velocityX > 1200.0f) {
            velocityX = 1200.0f;
        } else if (velocityX < 1200.0f) {
            velocityX = -1200.0f;
        }
        return super.onFling(e1, e2, velocityX, velocityY);
    }   
}

XML部分：

<ScrollableGallery
        android:id="@+id/gallery"
        android:layout_width="675dp"
        android:layout_height="492dp"
        android:layout_marginLeft="62dp"
        android:layout_marginTop="225dp"
        android:scaleType="fitXY" >
    </ScrollableGallery>

活动调用：
启动

final ScrollableGallery galleryView = (ScrollableGallery)findViewById(R.id.gallery);

适配器启动：

galleryV.setAdapter(new BaseAdapter() {                     
            public int getCount() {             
                return _imageList.size();
            }

            public Object getItem(int position) {
                return _imageList.get(position);
            }

            public long getItemId(int position) {
                _position = position;
                return position;
            }

            public View getView(final int position, View convertView,final ViewGroup parent) {              
                if (convertView == null) {
                    convertView = new ImageView(Database.this);
                }               
                ImageDispatcher dispatch = new ImageDispatcher(((ImageView) convertView));              
                dispatch.execute(_imageList.get(position));                                     
                ((ImageView) convertView).setScaleType(ImageView.ScaleType.FIT_XY);
                ((ImageView) convertView).setLayoutParams(new ScrollableGallery.LayoutParams(675, 492));

                return convertView;
            }           
        });
<br/>
The image dispatcher:

    import java.lang.ref.WeakReference;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.os.AsyncTask;
    import android.widget.ImageView;

    public class ImageDispatcher extends AsyncTask<String, Void, Bitmap> {

        private final WeakReference<ImageView> imageViewReference;

        public ImageDispatcher(ImageView imageView) {
            imageViewReference = new WeakReference<ImageView>(imageView);
        }

        @Override
        // Actual download method, run in the task thread
        protected Bitmap doInBackground(String... params) { 

            return ShrinkBitmap(params[0], 300 ,300);
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            if (isCancelled()) {
                bitmap = null;
            }

            if (imageViewReference != null) {
                ImageView imageView = imageViewReference.get();
                if (imageView != null) {
                    imageView.setImageBitmap(bitmap);
                }
            }
        }

        /*********************************************************
         * PRIVATE METHODS 
         *********************************************************/
        @SuppressWarnings("unused")
        private Bitmap ShrinkBitmap(String file, int width, int height) {
            BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options();
            bmpFactoryOptions.inTempStorage = new byte[16 * 1024];
            bmpFactoryOptions.inJustDecodeBounds = true;
            Bitmap bitmap = BitmapFactory.decodeFile(file, bmpFactoryOptions);
            int heightRatio = (int) Math.ceil(bmpFactoryOptions.outHeight / (float) height);
            int widthRatio = (int) Math.ceil(bmpFactoryOptions.outWidth / (float) width);

            bmpFactoryOptions.inSampleSize = heightRatio > 1 || widthRatio > 1 ? heightRatio : widthRatio;                  
            bmpFactoryOptions.inJustDecodeBounds = false;
            bitmap = BitmapFactory.decodeFile(file, bmpFactoryOptions);
            return bitmap;
        }

        @SuppressWarnings("unused")
        private Bitmap ShrinkBitmap(String file) {
            BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options();
            bmpFactoryOptions.inTempStorage = new byte[16 * 1024];
            bmpFactoryOptions.inJustDecodeBounds = true;

            Bitmap bMap = BitmapFactory.decodeFile(file);       
            Bitmap bMapScaled = Bitmap.createScaledBitmap(bMap,150, 100, true);

            return bMapScaled;
        }
    }

我认为这就是我这部分的所有代码， 现在的问题是：
我如何制作滚动条，及时显示一张图像，以及如何在加载图像时像在网络中那样显示加载指示器？？？

任何代码修复将不胜感激！

先感谢您...

Answer 1

而不是在 xml 中声明 Gallery。

Gallery gallery = new  CustomGaller(getActivity());

RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams  (LayoutParams.FILL_PARENT,LayoutParams.FILL_PARENT);
            params.addRule(RelativeLayout.RIGHT_OF, R.id.left);
            params.addRule(RelativeLayout.LEFT_OF,R.id.right);
            gallery.setLayoutParams(params);
            gallery.setAdapter(new GalleryAdapter(<Pass values>));

您不必将 View id 传递给 CustomGallery。

Answer 2

在您的自定义图库中

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,float velocityY) {
    -->> super.onFling(e1, e2, 20, velocityY); <<--

    return false;
}

尝试修改第三个参数。